This invention relates to door mechanisms, and more particularly to counterbalancing springs for heavy doors, ramps, gates or large structures such as garages and other buildings.
Many car garages, especially those in residential buildings, are equipped with doors that are opened by raising them from a vertical closed position to a horizontal open position. The doors, which are quite heavy, must be counterbalanced to permit reasonably easy opening and closing. The doors typically are of two types, pivoted doors, and track-guided doors.
The pivoted garage doors of the prior art, whether directly pivoted on a horizontal axis or indirectly pivoted by a multiple bar linkage mechanism, are usually counterbalanced by long, helical, closely wound tension springs.
There are several disadvantages with the conventional tension springs of the prior art. Tension springs are not very durable. They break after a certain amount of use as a result of overloading and/or metal fatigue. The breakage occurs usually while the spring is extended from the relatively relaxed open position as the door is closed. The danger of spring breakage is aggravated by the presence of adjustment devices in most prior art door mechanisms. In an effort to increase the counterbalancing force, the spring can be adjusted to a greater extension than it can safely stand, becoming overloaded when the door is closed. When breakage occurs, pieces and small metal fragments from the broken spring can fly through air, posing a serious danger to both life and property. The end portions of the broken spring can whip around, presenting additional dangers. Also, if the spring breaks while the door is being lifted or lowered, the loss of the counterbalancing tension provided by the spring can cause the door to come crashing down, again posing grave health hazards to a person operating the door.
Moreover, most of these garage door spring assemblies use helical tension springs with unsightly exposed coils. The coils separate when the spring is extended. There is always the danger that objects or fingers can be caught between the coils when tension is relaxed, causing damage or physical injury.
The track-guided doors of the prior art, whether of one-piece or folding construction, are usually connected on opposite sides by cables to respective lift drums of a transverse, rotatably mounted, overhead drive-shaft. Counterbalancing is typically provided by one or more elongated helical torsion springs that encircle the drive shaft. These doors have many of the above-described disadvantages of the pivoted doors. A further disadvantage is that the adjustment of the mechanism is specially awkward and dangerous because of its overhead location. Indeed, it is often required that the installation and adjustment of the overhead torsion springs be performed by specially licensed installers because they are so dangerous. Moreover, access to the drive shaft is typically blocked from below when the door is opened, and the mechanism has to be adjusted in the fully preloaded, closed position wherein there is the dangerous condition of maximum spring loading. Climbing above the open door is even more dangerous.
A further problem that is typical of both the pivoted and track-guided doors is that the installation and adjustment of counterbalancing springs is difficult and dangerous because high spring loading is present, especially when the door is closed. Often the door is propped open by makeshift means, subjecting a worker to a danger of the door crashing down during spring installation.
Thus there is a need for a door counterbalancing spring that is safe and reliable, inexpensive to make and install, neat in appearance, and capable of replacing conventional springs in existing installations. There is a further need for an improved counterbalancing system for track-guided doors.